Magnetic recording media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A conventional, single-sided, longitudinal magnetic recording medium 1 in e.g., disk form, such as utilized in computer-related applications, is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, metal-ceramic composite, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al--Mg), having at least one major surface 10A on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers typically include a plating layer 11, as of amorphous nickel-phosphorus (NiP), a polycrystalline interlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic recording layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., a diamond-like carbon (DLC), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound.
According to conventional manufacturing methodology, a majority of the above-described layers constituting magnetic recording medium 1 are deposited by cathode sputtering, typically by means of multi-cathode and/or multi-chamber sputtering apparatus wherein a separate cathode comprising a selected target material is provided for deposition of each component layer of the stack and the sputtering conditions are optimized for the particular component layer to be formed. Each cathode comprising a selected target material can be positioned in a separate, independent process chamber, in a respective process chamber located within a larger chamber, or in one of a plurality of separate, interconnected process chambers each dedicated for deposition of a particular layer. According to such conventional manufacturing technology, media substrates, e.g., disks, are serially transported, in linear or circular fashion, depending upon the physical configuration of the particular apparatus utilized, from one sputtering target and/or process chamber to another for sputter deposition of a selected layer thereon. In some instances, again depending upon the particular apparatus utilized, sputter deposition of the selected layer commences only when the substrate (e.g., disk) deposition surface is positioned in complete opposition to the sputtering target, e.g., after the disk has fully entered the respective process chamber or area in its transit from a preceding process chamber or area, and is at rest. Stated differently, sputter deposition commences and continues for a predetermined interval only when the substrate is not in motion, i.e., deposition occurs onto static substrates. In other instances, however, substrate motion between adjoining process chambers or areas is continuous, and sputter deposition of each selected target material occurs onto moving substrates as the substrates pass by the particular cathode/target assembly.
Regardless of which type sputtering apparatus is employed for forming the thin layer stacks constituting the magnetic recording medium, it is essential for obtaining high recording density, high quality media that each of the component layers be deposited in a highly pure form. Film purity depends, inter alia, upon the purity of the atmosphere in which the film is grown; hence films are grown in as low a vacuum as is practicable. If the growth rate is maintained constant, purity can therefore be increased by more effective pumping away of contaminant gases which enter the process chamber, either by outgassing or desorption from the chamber walls and other system components, permeation into the chamber through seals such as O-rings, or as impurities in the sputter gas, e.g., argon (Ar). Alternatively, increased film purity can be obtained by increasing the rate of growth to decrease the ratio of impurity atoms in the film to those of the intended deposit.
However, practical limitations exist with respect to increasing the deposition speed obtainable with conventional sputtering apparatus and manufacturing technology, whether the deposition is performed onto static or moving substrates. For example, the available technology imposes certain limits on the output of RF and DC sputter power supplies and transport speed of the substrates from one process chamber to another (via air-locks, etc.). More specifically, available technology cannot provide more than about a ten-fold ("10.times.") increase in sputtering power and more than about a three-fold ("3.times.") increase in transport speed. Moreover, since in a moving substrate process/apparatus, a 10.times. increase in deposition rate requires a corresponding 10.times. in transport speed past the target sputtering surface in order to maintain the produced film thickness constant at the desired or target value, it becomes apparent that the requisite increase in transport speed becomes the limiting factor in obtaining higher deposition rates on moving substrates. Since only an about 3.times. increase in transport speed is practically possible, it is evident that only a modest improvement in film purity is possible by increasing the sputtering power applied to the target.
In addition to the above-described need for deposition rates of high purity layers consistent with the productivity requirements imposed by automated manufacturing technology, it is also essential that each of the deposited films exhibit respective physical, chemical, and/or mechanical properties, including, inter alia, proper crystal morphology necessary for high recording density media, e.g., polycrystallinity; good magnetic properties, e.g., coercivity and squareness ratio; chemical stability, e.g., inertness or corrosion resistance; and good tribological properties, e.g., wear resistance and low stiction/friction.
Accordingly, there exists a need for improved methodology for forming, by sputtering techniques, thin film layers of high purity and desired physical, chemical, and/or mechanical properties, which methodology provides for rapid, simple, and cost-effective formation of thin film layers suitable for use in the manufacture of magnetic recording media comprising a plurality of stacked layers deposited on a suitable substrate surface.
The present invention addresses and solves problems attendant upon the use of sputtering techniques for obtaining high purity thin film layers having requisite properties, such as are utilized, inter alia, in the manufacture of high recording density magnetic recording media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology. Further, the methodology provided by the present invention enjoys diverse utility in the manufacture of a variety of devices and products requiring high purity thin film coating layers having desirable physical, chemical, and/or mechanical properties.
Disclosure of the Invention
An advantage of the present invention is an improved method for sputter depositing high purity thin film layers onto a substrate deposition surface.
Another advantage of the present invention is an improved method for sputter depositing high purity thin film layers having desired physical, chemical, and/or mechanical properties onto a substrate deposition surface.
Yet another advantage of the present invention is an improved method for sputter depositing high purity thin films having desired properties onto a static or moving deposition surface of a substrate.
Still another advantage of the present invention is an improved method for sputter depositing a layer stack comprising a magnetic recording medium.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a method of sputter depositing onto a substrate deposition surface a thin film layer comprising a target material, comprising:
(a) providing a substrate having a deposition surface; PA1 (b) providing a cathode including a target having a sputtering surface comprised of the target material, with the target sputtering surface facing the substrate deposition surface with a space therebetween; and PA1 (c) sputtering said target material onto the substrate deposition surface by applying a plurality of negative voltage pulses to the cathode while simultaneously applying a bias voltage to the substrate. PA1 (d) providing a plurality of cathodes each including a target having a sputtering surface comprised of a material to be sputter deposited onto the substrate deposition surface; PA1 (e) moving the substrate deposition surface along a path passing by each of the sputtering surfaces; and PA1 (f) sputtering each of the target materials onto the substrate deposition surface by applying a plurality of negative voltage pulses to each of the plurality of cathodes while simultaneously applying a bias voltage to the substrate, thereby depositing on the substrate deposition surface a layer stack comprising the recording medium. PA1 (a) providing a substrate having a deposition surface; and PA1 (b) sputter depositing the layer of material on the substrate deposition surface utilizing a sputter deposition apparatus including means for applying negative voltage pulses to a cathode target comprised of the material while simultaneously applying a bias voltage to the substrate.
According to an embodiment of the present invention, step (a) comprises providing a static substrate and step (c) comprises applying to the cathode a sufficient number of negative voltage pulses of sufficient power to sputter deposit a layer of desired thickness on the substrate deposition surface.
According to further embodiments of the present invention, step (c) comprises applying a constant bias voltage to the substrate, i.e., a constant positive or negative bias voltage; whereas according to still further embodiments of the present invention, step (c) comprises applying a pulsed bias voltage to the substrate synchronously with the negative voltage pulses applied to the cathode, i.e., a pulsed positive or negative bias voltage.
According to yet further embodiments of the present invention, step (c) comprises applying to the substrate first bias voltage pulses during the application of the negative voltage pulses to the cathode and applying to the substrate second, different bias voltage pulses during intervals when the negative voltage pulses are not applied to the cathode, e.g., applying to the substrate first and second bias voltage pulses which differ in voltage and/or polarity.
According to specific embodiments of the present invention, step (a) comprises providing a substrate for a magnetic recording medium and steps (b) and (c) are repeated with different target materials to deposit on the substrate deposition surface a layer stack comprising the magnetic recording medium.
According to another embodiment of the present invention, step (a) comprises providing a substrate wherein the deposition surface thereof moves past the target sputtering surface and step (c) comprises applying to the cathode a sufficient number of negative voltage pulses of sufficient power to sputter deposit a layer of desired thickness on the substrate deposition surface during the interval when the substrate deposition surface moves past the target sputtering surface.
According to further embodiments of the present invention, step (c) comprises applying a constant bias voltage to the substrate, i.e., a constant positive or negative bias voltage; whereas, according to still further embodiments of the present invention, step (c) comprises applying a pulsed positive or negative bias voltage to the substrate synchronously with the negative voltage pulses applied to the cathode.
According to yet further embodiments of the present invention, step (c) comprises applying to the substrate first bias voltage pulses during the application of the negative voltage pulses to the cathode and applying to the substrate second, different bias voltage pulses during intervals when the negative voltage pulses are not applied to the cathode, e.g., applying to the substrate first and second bias voltage pulses which differ in voltage and/or polarity.
According to specific embodiments of the present invention:
step (a) comprises providing a substrate for a magnetic recording medium, and the method further comprises:
According to further specific embodiments of the present invention, step (f) comprises depositing a layer stack including, in sequence from the substrate deposition surface, a polycrystalline underlayer, a magnetic recording layer, and a protective overcoat layer.
According to another aspect of the present invention, a method of sputter depositing a layer of a material on a substrate surface comprises:
According to a specific embodiment of the present invention, step (a) comprises providing a substrate for a magnetic recording medium.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.